Methods for grinding (or, in the jargon, arrissing) the edges of glass sheets in the condition in which they are after cutting into the final formats for use are currently known. In principle, arrissing can be applied to any step of the working of the glass sheets, for example before tempering.
Arrissing is performed for two reasons: the first relates to safety in handling the sheets, in which the edges would be dangerously sharp if they were not arrissed. The second reason relates to eliminating the edge defects of the sheets, typically so-called microcracks, which might trigger breakages of the sheet in the subsequent working steps (particularly during tempering) and also during subsequent use.
In order to better understand the configuration of the glass sheet, not so much in its possible isolated use but most of all in its use in combination with other components to constitute the so-called double glazing unit, some concepts related to the intermediate component, i.e., the glass sheet, and the final product, i.e., the double glazing unit, are summarized hereafter. The subsequent use of the double glazing unit, i.e., as a component of doors and windows, is known to the person skilled in the art and is not discussed here in detail.
With reference to FIG. 1, the double glazing unit is constituted typically by two or more glass sheets 1001, 1002, which are mutually separated by one or more spacer frames 1003, which are internally hollow and are provided with fine perforations on the face directed toward the inside of the chamber.
The spacer frames 1003 usually contain, in their hollow part, hygroscopic material, which is not shown in the figure. A chamber (or chambers) 1006 delimited by the sheets 1001 and 1002 and by the frame 1003 can contain air or gas or mixtures of gas injected therein, which give the double glazing unit particular properties, for example thermal insulation and/or soundproofing properties. Coupling between the glass sheets and the frame is achieved by means of two levels of sealing: a first seal 1004 is intended to provide a hermetic closure and affects the lateral surfaces of the frame 1003 and the portion that is adjacent thereto of the glass sheets 1001, 1002; a second seal 1005 affects the compartment constituted by the outer surface of the frame and by the faces of the glass sheets up to their edge and is intended to produce cohesion among the components and maintain the mechanical strength of their mutual coupling.
FIG. 1 shows five possible sectional views of configurations of double glazing units 1A, 1B, 1C, 1D, 1E, only the first of which has been commented. However, it is straightforward to extend the above description to configurations 1B-1E, in which there are several frames or several glass sheets, the latter being optionally laminated. In the figure, the sun represents schematically the outside environment of a building in which the double glazing units are installed, while the inside of the building is represented schematically by a radiator.
The glass sheets used in the composition of the double glazing unit can have different shapes depending on use: for example, the outer glass sheet 1001 (with respect to the building) can be normal or reflective (in order to limit heat input during summer months) or it can be laminated/armored (for intrusion prevention/vandalism prevention functions) or can be laminated/tempered (for safety functions) or combined, for example reflective and laminated.
The internal sheet 1002 (with respect to the building) can be normal or of the low-emissivity type (in order to limit the dispersion of heat during winter months) or can be laminated/tempered (for safety functions) or can be combined, for example low-emissivity and laminated.
The simple summary given above already clearly shows that a production line for obtaining a double glazing unit requires many processes in sequence and that in both the intermediate components (i.e., the glass sheets) and the end product (i.e., the double glazing unit), the edges of the glass sheets can be accessed for contact with the hands of operators and users. It is therefore important to increase safety by beveling the peripheral edges of the glass sheets. If the finished product, which has a considerable added value with respect to the individual sheet, had sheet edges that could cut or sheets with non-rounded edges, it would be degraded in terms of quality and commercial value.
The processes for producing the double glazing unit typically are numerous, and each one requires a corresponding and particular machine to be arranged in series with respect to the other complementary ones. By way of non-limiting example, some processes or operations, not all of which are necessary, are the following:
EDGING on the peripheral face of the glass sheet to remove any coatings, in order to allow and maintain over time the adhesion of the sealants;
WASHING of the individual sheets, alternating an internal sheet with an external sheet (the orientation being the one defined above);
APPLICATION OF THE SPACER FRAME: the frame, manufactured beforehand, filled with hygroscopic material and coated on its lateral faces with an adhesive sealant having sealing functions, is applied to one of the sheets that constitute the double glazing unit in a suitable station of the double glazing unit production line;
MATING AND PRESSING of the assembly constituted by the sheets and the frame (or frames);
FILLING WITH GAS of the chamber (or chambers) thus obtained;
SECOND SEALING.
The processes described above can be performed by the respective machine automatically or semiautomatically, but in any case they entail the contact of the intermediate components and of the finished products with the operator, for example in the steps for loading and unloading the line and in the subsequent steps for storage, transport, assembly and installation of the double glazing units.
As regards arrissing, which is not included in the list of processes described above, in the known manual method glass sheets, rested on supporting surfaces are placed in contact with belt arrissers, which are arranged sequentially and are angularly offset so as to bevel both edges of the side of the sheet (methods of this type are described for example in DE-A 44 19 963). EPA 0 920 954 describes an apparatus for beveling, by means of an automatic method, sheets of cut glass which uses a pair of abrasive belts.
The main drawbacks that arise from the known methods described above relate to the considerable bulk and cost of the machines, to the complex operations for process maintenance (such as the replacement of the abrasive belts), to the less than optimum quality of the arrissing operation, to the abnormal behavior of the belt in interaction with the glass when its width does not mate fully with the sheet (i.e., at the end of the side of the sheet), and finally the excessively long production times.
The Applicant of the present invention is also applicant of EPA 1 488 886, the invention device of which, designated as “machine for glass pane border grinding”, will be used, in one possible configuration, in combination with the subject of the present invention.